meta: support for inputs

Inputs are modules like Stages, Assemblers and Sources. Add them
as a new module klass to the various functions. Include them in
the schema test, so the schema of all inputs is validated.
Also sort the module classes alphabetically in the class mapping
and class list.

osbuild/meta.py

@@ -359,9 +359,10 @@ class ModuleInfo:
     @staticmethod
     def module_class_to_directory(klass: str) -> str:
         mapping = {
-            "Stage": "stages",
             "Assembler": "assemblers",
-            "Source": "sources"
+            "Input": "inputs",
+            "Source": "sources",
+            "Stage": "stages",
         }
 
         return mapping.get(klass)
@@ -419,7 +420,7 @@ class Index:
             with contextlib.suppress(FileNotFoundError):
                 with open(path, "r") as f:
                     schema = json.load(f)
-        elif klass in ["Stage", "Assembler", "Source"]:
+        elif klass in ["Assembler", "Input", "Source", "Stage"]:
             info = self.get_module_info(klass, name)
             if info:
                 schema = info.schema

test/mod/test_osbuild.py

@@ -124,7 +124,7 @@ class TestDescriptions(unittest.TestCase):
         index = osbuild.meta.Index(os.curdir)
 
         modules = []
-        for klass in ("Stage", "Assembler", "Source"):
+        for klass in ("Assembler", "Input", "Source", "Stage"):
             mods = index.list_modules_for_class(klass)
             modules += [(klass, module) for module in mods]